1. Field of the Invention
This invention relates to non-contact remote ultrasonic testing of railroad wheels. More particularly, this invention relates to a method for using a Laser-Air Hybrid Ultrasonic Technique (LAHUT) as a noncontact and remote ultrasonic system for testing railroad wheels.
2. Description of the Related Art
Railroad maintenance is one of the greatest problems facing the transportation industry today. In one four-month period in 1998, a major railroad company experienced ten derailments due to broken rail at an expense of over $1.3 million. In its Newsletter, in Sep. of 2000, the Texas Research Institute estimated that every ninety minutes a derailment, an accident, or any other rail related incident takes place in the U.S.
For decades, optical methods (i.e., laser generation and interferometric detection of ultrasound) have been widely popular as noncontact and remote detection techniques for identifying flaws in structural materials. However, their efficiency relies heavily on the amount of light reflected back from the surface. As a result, the curvature, roughness and cleanliness of the reflecting surface all have a negative influence on the amount of light reflecting back to the optical detector. This, unfortunately, renders these techniques ineffective for many industrial applications, including the railroad industry.
Other than by visual inspection, no technique is readily available today to the railroad industry to perform inspections on railroad wheels while they are still mounted on a train. Prior acoustic inspection techniques have proved to be unreliable.
For example, an attempt was made to automate the inspection of rail wheels of passing trains (See: M. N. Fahmy, R. E. Finch, “Cepstrum analysis of surface waves in acoustic signature inspection of railroad wheels”, J. Acoust. Soc. Am., Vol. 75 (4), April 1984, pp. 1283-1290) by striking the wheels with a set of hammers. As a result of the hammers' impact on the wheel, an acoustic wave was generated in the wheel and detected with air-coupled transducers. However, both the generating technique and the detecting transducer operated with low frequency sound, such that the signal was often indistinguishable from mechanical noise.
Today, wheels are inspected only when railroad cars are sent for maintenance in service shops. Only about 10% of the wheels are possibly inspected for flaws in service shops annually. There are approximately ten million rail wheels in service in the U.S.
The present inventors' early experiments utilizing non-contact, ultrasonic techniques for the inspection of railroad tracks and railroad wheels were initially disclosed in May 2000. See “Non-Contact Ultrasonic Inspection of Railroad Tracks,” 45th International SAMPE Symposium, San Diego, Calif., May 21-25, 2000. The teachings and disclosure of this work is hereby incorporated by reference. The experimental techniques of this early work used laser beams focused to a point. These early techniques will be seen to differ significantly from those revealed herein. The present inventors have also documented much of their work on the inspection of railroad tracks and wheels in the scientific literature. See “Laser-Air Hybrid Ultrasonic Technique for Railroad Wheel Testing,” Materials Evaluation, vol. 61(4) April 2003 pp. 505-511; “Laser-Based and Air Coupled Ultrasound as Noncontact and Remote Techniques for Testing Railroad Tracks,” Materials Evaluation, vol. 60(1), January 2002, pp. 65-70; “Point and Line Source Laser Generation of Ultrasound for Inspection of Internal and Surface Flaws in Rail and Structural Materials,” Research in Nondestructive Evaluation, vol. 13(4), December 2001, pp. 189-200, “Narrowband Laser-Generated Surface Acoustic Waves Using A Formed Source In The Ablative Regime,” Journal of Acoustical Society of America, vol. 113(1), January 2003, pp. 261-266, “Laser-Based and Air Coupled Ultrasound as Noncontact and Remote Techniques for Testing Railroad Tracks,” (Translated to Italian), The Journal of the Italian Society of Nondestructive Testing Monitoring Diagnostics, vol. 23(2), 2002, pp. 34-41, “Laser And Air-Coupled Transducer For Non-Contact Ultrasonic Inspection In The Railroad Industry (in Italian),” ENEA Trisaia Research Center (MT) Italy, “I1 Giornale delle prove nondistructive monitoraggia,” diagnostica, 1, 2003, pp. 27-32, “Laser-Air Hybrid Ultrasonic Technique for the Inspection of Rail Steel,” Nondestructive Characterization of Materials, Berlin, Germany. Jun. 24-28, 2002, pp. 27-31, and “Sensitivity of Point And Line Source Laser Generated Acoustic Wave To Surface Flaws,” IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, To Be Published 2003. The teachings and disclosure of these works are hereby incorporated by reference.
In view of the lack of viable techniques for inspecting rail wheels in the field and the significant losses that occur in railway accidents attributable to wheel defect problems, it is seen that a great need exits for a testing method that can inspect rail wheels in the field.
3. Objects and Advantages
There has been summarized above, rather broadly, the prior art that is related to the present invention in order that the context of the present invention may be better understood and appreciated. In this regard, it is instructive to also consider the objects and advantages of the present invention.
It is an object of the present invention to provide a testing method for inspecting railroad wheels in the field.
It is another object of the present invention to provide a testing method that can test the railroad wheels of a stationary or moving train car.
It is yet another object of the present invention to provide a railroad wheel testing apparatus that can be maintained clear of the rail track and any obstacles along the test path.
It is a further object of the present invention to provide an ultrasonic railroad wheel testing method and apparatus that operates without establishing any contact with the surface of a rail wheel.
It is a still further object of the present invention to provide a rail wheel testing method and apparatus that provides superior signal-to-noise ratio (SNR) to that achieved with other non-contact ultrasonic methods, such as Electro-Magnetic Acoustic Transducers (EMATs) or measurements obtained with optical detection techniques of stress waves.
It is an object of the present invention to provide a rail wheel testing apparatus and method that allows for complete rail wheel inspection, on a moving or stationary rail car, including hard-to-reach areas such as the back surface (field-side) of the wheel.
It is another object of the present invention to provide an ultrasonic railroad wheel testing apparatus and method that detects both surface breaking and internal anomalies.
It is yet another object of the present invention to provide a rail wheel testing apparatus and method whose test signals can be processed via advanced signal analysis methods (e.g., frequency, feature extraction, wavelet and signal classifier methods) so as to enable automated signal recognition at rates not possible by manual means.
These and other objects and advantages of the present invention will become readily apparent as the invention is better understood by reference to the accompanying summary, drawings and the detailed description that follows.